Photovoltaic systems use photovoltaic panels to convert sunlight into electricity. A photovoltaic system may contain one or more inverters, also known as a direct current (DC) to alternating current (AC) power converters. Electricity generated by a photovoltaic system may be stored, directly used, fed into a power grid, or combined with other power generators.
Inverters used in photovoltaic systems may include stand-alone inverters, grid-tie inverters, and battery backup inverters. Stand-alone inverters are used in isolated systems where the inverter draws DC energy from batteries charged by the photovoltaic system. Battery backup inverters are designed to draw energy from a battery, manage the battery charge, and export excess energy to the power grid. Some inverters may use maximum power point tracking (MPPT) to convert the maximum power from the DC input to the AC output.
Grid connection inverters supply AC power in a sinusoidal form synchronized to the power grid at the grid frequency, where the voltage is capped at the grid voltage. The AC output is disconnected from the grid if the grid voltage is turned off to provide anti-islanding protection. Thus, grid connection inverters do not provide back-up power during utility outages. An island exists when power is fed to a small section of the power grid, and may present a risk to workers who expect the area to be unpowered. Also, without a grid signal to synchronize to, the power output of the inverters may drift from the tolerances required by customer equipment connected to the island.